Recording medium having an image receiving coating of a thermoplastic epoxy resin



July 28, 1964 A. KATCHMAN 3,142,585

RECORDING MEDIUM HAVING AN IMAGE RECEIVING COATING OF A THERMOPLASTICEPOXY RESIN Filed Oct. 50, 1961 EPOXY RES/IV CONDUCT/1V6- LAYE-RTHERMOPLASTIC LAYEI? HE'ATRES/STANT SUPPOR TING BASE MEMBER I 7'? ve r7to 2-.-

Ar'shur' Katchman,

is Attorney.

United States Patent 3,142,585 RECORDING MEDIUM HAVHPJG AN IMAGE PCEIVENG COATENG OF A THERMLOELASTIfi EPUXY REEalN Arthur Katehman,Schenectady, N.Y., assignor to General Electric ompany, a corporation ofNew York Filed Oct. 30, 1961, Ser. No. 148,464 6 Claims. ((31. 117-211)This invention is concerned with compositions of matter and articlesprepared therefrom useful in the recording, storing and reproducing ofphotographic images, technical data, etc. More particularly, theinvention relates to a recording medium comprising a base supportingmember and a thermoplastic layer thereon comprising a solid epoxy resincontaining epoxy groups having an average molecular weight between 1500and 4000 (hereinafter referred to as epoxy resin) and being the productof reaction of a polyhydric organic compound, e.g.,2,2'-bis(p-hydroxyphenyl) propane (also known as hisphenol A), and anepihalohydrin, such as epichlorohydrin. Such compositions derived frombisphenol A can be considered as having the formula (I) where n is anumber (usually a whole number) having an average value equal to aboutfrom 4 to 12, inclusive. The recording media can be in the form offilms, for instance, tapes, sheets, etc., as well as slides, disks,etc., which are suitable for recording, storing and reproducingphotographic images and technical data, employing the above epoxy resinas the thermoplastic layer in which such images and data are recorded,stored and reproduced.

in the copending applications of William E. Glenn, In, Serial No.698,167, filed November 22, 1957, and Serial No. 783,584, filed December29, 1958, now abandoned, both of which are assigned to the same assigneeas the present invention, are disclosed and claimed an electronic methodand apparatus for recording, storing and reproducing photographic imagesand technical data. According to this method, technical data andphotographic images are first converted electronically into codedsignals which are further reduced to variations in the intensity of abeam of electrons, and the electron beam with its negatively chargedparticles is used to scan a special surface so as to introduce onto thissurface a pattern of negative charges (from the electrons deposited)which arrange themselves in accordance with the data or image to berecorded. This pattern of electric charges on the heat-deformablethermoplastic layer is then converted to a pattern of depressions,ridges, etc., that can be observed optically.

This conversion can be achieved by heating the composite article orrecording medium, particularly the surface thereof with, for instance,direct application of heat or by heat generated by radio frequencyenergy acting on a conducting layer, whereby the heat causes only thetop thermoplastic negatively charged layer to fuse or melt, and becomeliquid. When this happens, the negative charges are attracted to theconducting layer positioned under but not necessarily in contact withthe thermoplastic layer, thus deforming the surface of the thermoplasticupper layer into various depressions, hills, ridges, etc. Thereafter,the heated surface is cooled or allowed to cool immediately to set orsolidify these hills, ridges, and other deformations in thethermoplastic layer. The recording medium thus treated can now be reador projected visually by passing a beam of light through it incooperation with a special optical system for conversion into an imageor can be optically converted into the de 3,142,585 Patented July 28,1964 sired information or data in the form of electrical signals. heimage can be viewed directly, projected on a screen, transmittedelectronically for viewing on a television screen elsewhere, or can besimply stored on film. An additional description of the method forrecording in the manner described above can be found in an article byWilliam E. Glenn, Jr., in Journal of Applied Physics," December, 1959,pages l8701873.

Because the thermoplastic layer is capable of being heated to the liquidstate (at which time it develops the surface deformations by action ofthe induced electric field on a charged portion of the liquid and thepattern of ripples thus produced frozen into a permanent record bypromptly cooling the liquid thermoplastic layer to the solid state), itis possible to employ such recording material many times by merelysubjecting the surface layer to the action of heat at a temperature highenough to cause fusion of the upper layer to a smooth surface, thuserasing the information stored in the aforesaid thermoplastic layer. lnaddition to the ability to reuse the recording medium, the latter canalso be employed as a master copy for duplication by techniques similarto phonograph disk stampings.

There are several requirements which are necessary for a satisfactoryrecording medium (recording medium or recording material willhereinafter be intended to mean the composite structure including theupper thermoplastic layer upon which the information is recorded andused in the electronic recording previously described, the basesupporting layer and the conducting layer if it is part of the compositestructure). In the first place, the recording medium must have opticalclarity and must be transparent. It is preferably water-white (i.e.,water-clear) or only slightly tinted in thin films. Any trace of hazeshould be avoided in the recording medium because it will interfere withthe later reading out or projection of any images which may have beenintroduced into the recording medium.

The recording medium must also have certain electrical characteristics,particularly it must be a good insulator and have high electricalresistivity; usually it is desirable that the specific resistivity begreater than about 10 oh1ncentimeters when in the liquid state at thetime it is heated to effect formation of any depressions or ridges orother deformations in the surface thermoplastic layer.

In addition, for certain applications, particularly in tapes, therecording medium, including the surface thermoplastic layer, must besufficiently flexible and strong to enable it to be rolled up aroundsmall diameters especially when the thermoplastic layer is present inthicker than usual sections. These are the usual requirementsencountered in the case of projection machines, for instance,16-millimeter projection machines which may be used to project the imageon the screen.

The thermoplastic layer of the recording medium must be stable undermoderate electron bombardment from the electron high voltageaccelerating apparatus. The thermoplastic layer preferably has a maximumvapor pressure of 10* to 10 mm. Hg when in the liquid state, that is,when it is subjected to the elevated temperatures required to deform thethermoplastic layer of the recording medium in accordance with thechanges thereon. The thermoplastic layer must also be stable at elevatedtemperatures at which it will be deformed by the heat necessary todevelop the charge on the thermoplastic layer.

Of major importance, the thermoplastic layer of the recording mediummust be capable of having a fairly -a polystyrene, and mixtures of (a)and (b).

sharp melting point in order that the developing of the proper image onthe thermoplastic layer proceed with a minimum of control difiiculties.For a broad spectrum of use, the thermoplastic layer should be solid attemperatures of at least 65 C., but should be capable of being convertedto the liquid or fused state at temperatures of at least about 85 C.depending on the supporting backing layer.

Since the recording medium may comprise at least two layers and moreoften three layers, it is also essential that the thermoplastic layerhave good adhesion to the backing material, whether it is the supportingbacking or the conducting layer. Since one embodiment of the recordingmedium comprises a three-layer structure composed of the backingmaterial, the upper surface thermoplastic layer and an intermediateconducting layer (for instance, a thin film of metal, or a metal oxide,or a metal salt), it is additionally important that the thermoplastic'layer have good adhesion to the conducting layer or the conductingsurface.

As a further requirement, it is important in those cases where therecording medium will be in the form of a tape and thus will be rolledupon itself and stored, that the thermoplastic layer be substantiallyfree of cold flow that will cause any change in the configuration of therecorded information on the thermoplastic surface, such as anydepressions or hills or other deformations on the surface of thethermoplastic layer. Since the storage might take place under conditionswhere the temperature might rise to as high as 40 C. to 50 C., this coldfiow must be non-existent or very low even at these temperatures. Anysignificant cold flow may render the tape incapable of storage in reelcondition as is the usual movie film. As a still further requirement, itis essential that the thermoplastic layer have good resistance towardsoxygen attack so that it maintains high electrical resistivity duringprocessing of the tape. Again, in those cases where a tape is involved,and because the tape may be rolled up on itself, it is also essentialthat the thermoplastic layer should be non-tacky and should not stick toitself or to any other surface with which it might come in contact inthe rolled-up state.

Although thermoplastic compositions are described in the aforementionedpending applications of William E. Glenn, Jr., Serial Nos. 698,167 and783,584, now abandoned, it has been found that these thermoplastic materials do not have a sharp enough fusion point to the liquid state of thethermoplastic layer; furthermore, there is much to be desired in theadhesion of the thermoplastic layer to the conducting layer.Additionally, it has been found that the thermoplastic layer should bemore flexible in those instances where the recording medium would bewound around small diameters such as in the case of spindles andsprockets used in projection equipment. As a still further area ofimprovement, the thermoplastic layer should resist adhesion to theadjacent back of the base layer when the film is in the rolled-up state,for instance, as a reel, or a spool, etc.

A recording medium which employs a thermoplastic layer embracing theabove-mentioned desirable characteristics is found described and claimedin the copending application of Edith M. Boldebuck, Serial No. 8,587,filed February 15, 1960, and assigned to the assignee of the presentinvention, now US. Patent 3,063,872, issued November 13, 1962. In thisBoldebuck application, the recording medium contains as thethermoplastic layer, a solid heat deformable mixture of ingredientscomprising (1) an organopolysiloxane and (2) a thermoplastic, solid(i.e., solid at room temperature) aryl polymer selected from the classconsisting of (a) polyarylene ethers, (:1) though these thermoplasticcompositions have been found to be useful and to possess improvedproperties over thermoplastic layers previously employed in theabove-de- 4- scribed recording media, nevertheless certain difiicultieshave arisen in connection with the use of these thermoplasticcompositions for the recording medium.

In the first place, the Boldebuck thermoplastic layer is composed of amechanical mixture of ingredients contain ing at least two preformedcompositions, namely, the organopolysiloxane and the aryl polymer. It isobvious that the use of two such materials for a thermoplasticcomposition introduces many control problems in preparing thesecompositions and insuring that the properties and characteristics ofeach of the ingredients satisfies specifications designed to render thethermoplastic composition 0ptimum for use as a thermoplastic layer.Furthermore, the compositions used for the thermoplastic layer in theBoldebuck recording medium are relatively expensive materials and add tothe cost of the recording medium. In addition, it has also been foundthat the thermoplastic composition used in the Boldebuck application hasreduced flexibility when used in thicker sections so that the ability tobend films containing thicker sections of the Boldebuck compositionsover small diameters, for instance, over inch to /a inch diametermandrels, is materially reduced.

This is an undesirable characteristic when it is desired to useprojection machines for recording medium tapes in which the sprocketscarrying the film are extremely small. Finally, the means for makingeach of the polymeric elements comprising the Boldebuck thermoplasticlayer requires extensive processing and careful control of the process,thus again adding to the cost of the ultimate recording medium.

Unexpectedly, I have discovered that in addition to the desiredimprovements for the thermoplastic layer which have been referred toabove, I am also able to overcome the dificulties which have arisen inconnection with the use of a thermoplastic recording medium composed ofan organopolysiloxane and the aryl polymer, by employing as thethermoplastic layer an epoxy resin, for example, of the characterrecited in Formula I. In addition to obviating the difficulties recitedabove, it has also been found that improvements are noted in the abilityto coat the base member eitl er with or without the conducting layerover that resulting from trying to coat the base member with previouslyknown thermoplastic compositions for recording media of the typedescribed above.

It is accordingly one of the objects of this invention to preparerecording media using as the thermoplastic layer for recording, storingand reproducing photographic images, technical data, etc., a singlecomposition rather than a mechanical mixture of compositions.

It is another object of the invention to prepare recording media inwhich the thermoplastic layer thereon is sufficiently flexible so as tobe capable of being wound around extremely small diameters even when inthick sections without cracldng or in any way separating from thesubstrate to which it is applied.

An additional object of the invention is to prepare a recording mediumin which the thermoplastic layer on which information will be recordedand stored will have no undesirable afiinity for the base layer withwhich it may come in contact in a rolled up state and will show noundesirable cold flow when subjected to the pressures which may beencountered in the case of film maintained for long periods of time inthe rolled up state.

Other objects and the invention will become more apparent from thediscussion which follows.

The epoxy (or ethoxyline) resins used in the practice of my inventioncan be defined as a complex epoxide resin comprising a polyetherderivative of a polyhydric aromatic organic compound containing epoxygroups (and usually hydroxyl groups) are disclosed in various places inthe art. Among such references may be mentioned the aforesaid CastanPatent 2,324,483, Cass Patent 2,683,- 131, as well as Castan Patent2,444,333, British Patents 518,057 and 579,698. For the most part theseethoxyline resins are based on the resinous product of reaction betweenan epihalogenohydrin, for instance, epichlorohydrin, and a phenol havingat least two phenolic hydroxy groups, for example,bis-(4-hydroriyphenyl) dimethylmethane. US. Patents 2,494,295, 2,500,600and 2,511,913 also describe examples of ethoxyline resinous compositionswhich may be employed in the practice of the present invention. Byreference, the aforementioned patents are intended to be part of thepresent description of the ethoxyline resins used and, for brevity, theethoxyline resins will not be described other than that they containmore than one ethylene oxide group, e.g., from 1 to 2 or more epoxidegroups, per molecule, and may be prepared by effecting reaction betweena polyhydric phenol, for example, hydroquinone, resorcinol, condensationproducts of phenols with ketones, for instance,bis-(4-hydroxyphenyl)-2,2-propane, with epichlorohydrin, etc. Forexample, the reaction of epichlorohydrin withbis-(4-hydroxyphenyl)-2,2-propane may be formulated as follows:

inertness and resistance to radiation are polycarbonate resinscorresponding to the formula 0 (gigs [(idz ((13080 E where R is hydrogenor a monovalent hydrocarbon radical, many examples of which have beengiven above for R (where more than one R is used, they may be the sameor different); R is selected from the class consisting of alkylene andalkylidene residues (e.g., methylene, ethylene, propylene, propylidene,isopropylidene, cyclohexylidene, etc), oxygen, etc. C is the residue ofan arcmatic nucleus, (e.g., benzene, naphthalene, biphenyl, etc.nucleus); Y is a substituent selected from the group consisting of (a)inorganic atoms, (b) inorganic radicals, and (0) organic radicals, (a),(b) and (c) being inert to and unattected by the reactants and reactionconditions,

Alkali wherein n has an average value recited above. Many of these epoxyor ethoxyline resins are sold under the name of Epon resins by ShellChemical Corporation, or Araldite resins by the Ciba Company.

The thermoplastic epoxy resin composition advantageously has a numbermolecular weight within the range of from about 1500 to 4000 whenmeasured cryoscopically. Under many conditions of use, it is desirablethat the thermoplastic epoxy resin have a stick temperature of 6590 C.,a fluid temperature (i.e., becomes a fluid) or" about 105-115" C., andwhen used on a recording tape have sufiicient flexibility to be able tobe wound around a mandrel as small as A to inch in diameter withoutcracking.

The backing material for the recording medium may be either a flexiblecomposition or may be a rigid inflexible material. Examples of rigidmaterials which can be employed (keeping in mind that optical clarity,heat resistance, and radiation resistance are usually the requiredproperties) are, for instance, glass (in the form of plates, slides,disks, etc); unsaturated polyester resins (formed from the reaction of apolyhydric alcohol, such as ethyl ene glycol, diethyl glycol, propyleneglycol, dipropylene glycol, etc., and an alpha-saturatedalpha-beta-dicarboxylic acid or anhydride, for instance, maleic acid,maleic anhydride, fumaric acid, citraconic acid, etc); combined withthese unsaturated polyesters one may also incorporate suchcopolymerizable cross-linking ingredients, such as diallyl phthalate,diethylene glycol dimethacrylate, etc. One can also employ metals suchas aluminum, nickel, chromium, etc., where the metal serves both as aconducting layer and as a reflective surface which can be read opticallyby reflection.

Examples of flexible materials which can advantageously be employed asthe backing material are, for instance, polyethylene terephthalate(which can be obtained by the transesterification of esters ofterephthalic acid with divalent alcohols, for example, ethylene glycolas shown in US. Patent 2,641,592, Hofrichter), such polyethyleneterephthalate being sold by E. I. du Pont de Nemours and Company, ofWilmington, Delaware, under the name of Mylar. A more refined grade ofpolyester terephthalic acid tape or film found highly appropriate as thebasis for recording images (and which contains small intercondensedresidues from dihydric alcohols, such as, propylene glycol-1,3 to reducecrystallinity) is sold under the name of Cronar.

Another backing, material which can be used advantageously because ofits good heat resistance, strength,

e is a whole number equal to from 0 to a maximum determined by thenumber or" replaceable nuclear hydrogens substituted on the aromatichydrocarbon residue C; t is a whole number equal to from O to a maximumdetermined by the number of replaceable nuclear hydrogens on R and w isa whole number equal to from 0 to 1, inclusive. These compositions anddirections for preparing these compositions are disclosed and claimed inthe copending application of Daniel W. Fox, Serial No. 520,- 166, filedJuly 5, 1955, and assigned to the same assignee as the presentinvention. By reference, this application is made a part of thedisclosures and teachings of the instant application. It will beapparent to those skilled in the art that other compositions may beemployed as backing materials where the softening point is sufficientlyhigh so as to allow heating of the thermoplastic layer without adverselyafiecting the base layer.

In many instances, there is interposed between the thermoplastic surfaceand the backing, a conducting layer which can be subjected to radiofrequency energy as a means for heating the thermoplastic layer. Thisconducting layer acts as the layer which becomes positively chargedbeneath the thermoplastic layer and when the thermoplastic layer isheated to cause the thermoplastic material to become iiuid anddeformable, the deposits of negative charges on the top of thethermoplastic layer are attracted to the positively charged conductinglayer, thus deforming the thermoplastic surface of the film. Among suchconducting layers (which should be thin enough to be optically clear itinterposed between the base and the thermoplastic layer) may bementioned the various metals, for instance, iron, chromium, tin, nickel,etc.; metallic oxides, such as stannic oxide, cuprous oxide, etc.;salts, for instance, cuprous iodide, etc. In using the conducting layer,it is essential that the layer of metal or metal compound applied to thebase layer be no thicker than is required to obtain a transparent filmthereon. For this reason, it has been found that the metal film isadvantageously of the order of about 10 to Angstroms (A.) or 0.001 to0.01 micron thick, and that it should have a resistivity of between1,000 and 10,000 ohms per square centimeter for optimum radio frequencyheating it that is the method used for developing the deformationpattern.

The thickness of the thermoplastic layer can vary widely butadvantageously is approximately 4 to 20 microns thick. The base layerthickness can also vary widely as long as it has the proper electricaland radiation resistance flexibility, strength, heat resistance, etc.;this base 41 layer can be from a few microns in thickness to as much as50 to 400 microns or more in thickness.

The conducting layer is advantageously applied to the backing by thewell-known method of volatilizing the metal or metal compound in avacuum at elevated temperatures and passing the-backing in proximtiy tothe vapors of the metal or metal compound so as to deposit an even,thin, optically clear, adherent film of the metal or metal compound onthe backing and preferably while the entire assembly is still undervacuum. One method for applying a metal salt conducting layer to thebacking, e.g., polyethylene terephthalate, is found in US. Patent2,756,165, Lyon. Thereafter, a solution of the thermoplastic compositionis applied to the surface of the conducting layer, and the solventevaporated to deposit a thin film of the thermoplastic composition onthe conducting layer.

The particular solvents employed for the thermoplastic composition maybe varied Widely. Included among such solvents are methyl ethyl ketone,acetone, dibutyl ketone, aromatic hydrocarbon solvents, e.g., toluene,benzene, etc. Solids weight concentrations of from 10 to 30 percent ofthe thermoplastic composition in the solvent are advantageously used.

In the accompanying drawing, the single figure shows a tape recordingmedium composed of an upper thermoplastic layer 1 comprising an epoxyresin, a base member 2 supporting the thermoplastic layer, and anintermediate conducting layer 3.

The following examples are given by way of illustration and not by wayof limitation, as to how the present invention may be practiced. Allparts are by weight unless otherwise noted.

The liquid temperature of the thermoplastic compositions described beloware determined by placing on a melting point block a sample ofchromium-coated polyethylene terephthalate film (Cronar film), on whicha film of the thermoplastic composition had been deposited and thesolvent evaporated. The thermoplastic surface was scratched with aneedle as the temperature was gradually raised, and the temperature atwhich the thermoplastic epoxy resin flowed in immediately to obliteratethe scratch was recorded as the liquid temperature.

The number average molecular weight was determined cryoscopically. Thestick temperature of the epoxy resin was determined by heating the tapewith the epoxy resin composition on the surface and bringing thepolyethylene terephthalate backing into contact with the heated epoxyresin surface and determining the temperature at which the epoxy resinsurface stuck or caught on to the U applied backing.

The actual writing on the thermoplastic surface (which was about 712microns thick) was carried out as follows. An electron gun was mountedin an evacuated apparatus (described in the Glenn applications)containing an infrared heater. The optically clear tape was passed overthe heater and while the thermoplastic layer was in the molten condition(as a result of heating the tape to a temperature of about 90-100 C.),it was exposed to the electron beam. The electron beam was controlled tosweep back and forth in a linear path as the tape was passed under thebeam. While the beam was operated at a current of 1 microamp with a 6kv. accelerating potential drop from filament to ground plane (i.e., theconducting layer) about & of a second was required to inscribeinformation in an area of about 0.225 inch by 0.155 inch) for a singleimage by 262 /2 sweeps of the electron beam. The thermoplastic layer wasthen allowed to cool (while still in vacuum) to set or freeze thedeformations in the surface of the thermoplastic layer.

The epoxy resin used in Example 1 (sold as Epon 1004 by Shell ChemicalCorporation, New York, New York) was obtained by the reaction ofbisphenol-A and epichlorohydrin, and had an average molecular weight of1850, a melting point of 95105 C., an epoxy value equivalent per gramsof 0.11, and a hydroxyl value equivalent per 100 grams of 0.34.

Example 1 A 24 weight percent benzene solution of the above epoxy resinin methyl ethyl ketone was coated onto a 0.001 micron thickchromium-coated surface deposited on 30 mm. wide by 0.004 inch thickoptical grade polyethylene terephthalate tape sold as Cronar by E. I. duPont de Nemours and Company (methods for preparing such film may befound disclosed in such patents as US. 2,678,285 and 2,698,291). Afterremoving the solvent by first air-drying and then by heating for about10 or 15 minutes at about 150 C., it was found that the epoxy resinlayer was about 9 to 10- microns thick. The thermoplastic layer had afluid temperature of about 9S105 C. and a stick temperature of about100405 C. The above-coated recording medium could be bent around a inchdiameter mandrel without any evidence of cracking of the film or crazingthereof, or separation of the thermoplastic layer from the chromiumcoating. This optically clear recording medium when written upon in themanner described above and in the Glenn applications and when projectedgave well-defined images.

Example 2 In this example a 25 weight percent solution in methyl ethylketone was prepared of a mixture of the epoxy resin described above andof another epoxy resin (Epon 1007 manufactured by Shell ChemicalCompany) obtained by the reaction of bisphenol-A and epichlorohydrin,but this time the latter epoxy resin had an average molecular weight ofabout 3000, an epoxy equivalent value per 100 grams of 0.05 and ahydroxyl value equivalent per 100 grams of 0.36. The combined mixture ofepoxy resins had an average molecular weight of about 2600. These twoepoxy resins were mixed in about equal parts by weight to make up the 25percent weight solution in the methyl ethyl ketone. Again the solutionwas applied to the chromium-coated Cronar film similarly as was done inExample 1 to a thickness of about 7.5 microns. After removal of thesolvent, it was found that the thermoplastic epoxy resin coating had astick temperature of about 90100 C. and a fluid temperature of 1l5120 C.The optically clear recording medium could be bent around a inchdiameter mandrel without any evidence of cracking, crazing or separationof the thermoplastic layer from the chromium substrate. When thisoptically clear recording tape was written on in the same manner as wasdone in connection with the tape of Example 1, and thereafter projected,well-defined images were obtained.

Each of the thermoplastic coated tapes described in Examples 1 and 2could be readily erased by the application of heat to remove thedeformations which were present on the thermoplastic surface. Oneadvantage of these epoxy resins as the thermoplastic layer on therecording medium described above is revealed by the fact that they canbe treated with various curing or crosslinking agents such as ethylenediamine, diethylenetriamine, triethylene tetraamine,2,4,6-tri-(dimethylaminomethyl) phenol, etc. to effect crosslinking ofthe epoxy resin layer and to make permanent the record which wasinscribed there by means of the electron beam treatment and developmentof the electrical charges. The record thus induced was permanent becauseno reasonable amount of heat could effect erasure of the recorded imageas was possible when the recording layer was of a thermoplastic nature.The following example illustrates the use of amines as curing agents forthe thermoplastic epoxy resin and for making permanent the recordtherein inscribed.

Example 3 The optically clear recording medium described in Example 1was coated on the side of the epoxy resin layer with a 50 percent weightsolution in methanol of diethylenetriamine. The tape was then placed inan oven at about 40 C. for 20 minutes and upon removal the coating wasfound to be insoluble in methyl ethyl ketone and the images which hadbeen present in the thermoplastic layer could not be removed by heatingin an oven even at temperatures as high as 125 C. for one hour. It wasalso found that despite the insolubility and infusibility introduced bymeans of the treatment with the amine curing agent, neither theflexibility nor the adhesion of the epoxy resin surface was in any wayaffected.

Example 4 When an epoxy resin of an average number molecular weightbetween 2000 to 3000 was prepared from resorcinol with epichlorohydrin(employing the same conditions for making this resin as are used formaking the resin from epichlorohydrin and bisphenol-A) was applied to achro mium coated polyethylene terephthalate tape to a thickness of about8 to 10 microns similarly as was done in the above-identified examples,and the thermoplastic surface written on in the manner described above,there was obtained a recording medium which could be projected on ascreen to give well-defined images. The thermoplastic coating on thefilm is flexible and can be bent around small diametered mandrelswithout undesirable cracking or crazing.

Example 5 In this example, on a weight basis, 90 percent of a diphenylsilicone, and percent of a dimethyl phenylene ether polymer havingrecurring units of the formula l l l. ..i (these ingredients beingprepared in accordance with the directions described in theaforementioned Boldebuck application) were intimately mixed together ina toluene solvent. A sample of this solution in about a 25 weightpercent concentration was applied to a chromium-coated polyethyleneterephthalate film to a thickness of about 8 to 10 microns, and thecoating dried. Attempts to bend this film around a to 1 inch diametermandrel resulted in cracking of the film. As the thickness of thethermoplastic layer (composed of the two ingredients) increased, and thediameters of mandrels around which the tape could be bent withoutcracking or other evidence of deterioration were greatly increased.

It will, of course, be apparent to those skilled in the art that inplace of the epoxy resins used in the previous examples, one can employother epoxy resins, examples of which have been given above, withoutdeparting from the scope of the invention.

It is also desirable that the hydroxy substitution on the aromaticnucleus of the polyhydric aromatic compound be in the para or metapositions in order to attain the desired molecular weight which isrequired for obtaining the optimum properties of the thermoplasticcoating when deposited on the substrate or on the metal or otherwisecoated substrate. Thus, the hydroxy groups on the hisphenol-A or theresorcinol (or hydroquinone) are para or meta to each other or to anylinking group attached to the aromatic nucleus, e.g., the -C(CH group ofthe bisphenol-A.

Various modifying agents which do not adversely affect the propertiesrequired for the thermoplastic recording medium can be employed as, forinstance, various plasticizers to raise or lower the liquid meltingpoint of the thermoplastic layer, etc. In place of the polyethyleneterephthalate other backings can be employed as, for instance, thepolycarbonate resins heretofore recited.

The thermoplastic compositions and tapes made therewith can be employedin various applications and are particularly useful for recording ofcomputer information.

In addition, they can be used in the movie film industry whereby thesetapes can be used to record the action being filmed and the image can beprocessed immediately after the action has been recorded on the film andby suitable optical apparatus transferred and projected to determinewhether the action which was taken with the film is acceptable andsatisfactory for final showing.

Additional directions for using recording media of the type described inthe instant application can be found in the copending application ofWilliam E. Glenn, In, Serial No. 8,842, filed February 5, 1960, now U.S.Patent 3,113,179, and assigned to the same assignee as the presentinvention.

Instead of heating the tape in the irradiation apparatus as was done inthe preceding examples, the electron recorded information can bedeveloped by outside heat treatment. One method comprises applying acurrent or blast of hot air to the surface of the charged thermoplasticlayer where the temperature of the air is sufificiently high to effectliquefication of the thermoplastic layer to the desired degree offlowability to cause the deformation on the surface thereof; anothermethod comprises using radio frequency heating to arrive at the propertemperature for causing deformation of the surface of the thermoplasticlayer; and finally, particularly when a tape is employed, the tape ispassed over a heated drum maintained at the proper temperature whereinthe surface of the base member furthest from the thermoplastic layer isin direct contact with the heated drum so that heat diffuses upwardthrough the tape to the thermoplastic layer to cause the above-mentionedfusion and flowability of the latter.

The polyethylene terephthalate tape employed in the preceding examplesand the methods for manufacturing this particular tape are moreparticularly disclosed in U.S. Patents 2,465,319, Whinfield et al.,issued March 22, 1949, and 2,779,684, Alles, issued January 29, 1957.The latter Patent 2,779,684 recites in greater detail the processing ofpolyethylene terephthalate film employed in the manufacture of theaforesaid Cronar.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. An optically clear recording film consisting essen tially of (a) aflexible, transparent, heat resistant, polymeric base supporting member,(1)) a thermoplastic layer consisting essentially of a solid complexepoxide resin of average molecular weight between 1500 to 4000containing epoxy groups and comprising a polyether derivative of apolyhydric aromatic compound containing at least two phenolic hydroxygroups, and (c) an intermediate transparent conducting layer between thebase member and the thermoplastic layer.

2. An optically clear recording film consisting essentially of (a) aflexible, transparent, heat resistant, polymeric supporting base member,(b) a thermoplastic layer consisting essentially of a solid complexepoxide resin of average molecular weight between 1500 to 4000comprising the product of reaction of epichlorohydrin and bis-(4-hydroxyphenyl)-2,2-propane, and (c) an intermediate transparentconducting layer between the base member and the thermoplastic layer.

3. An optically clear recording film consisting essentially of (a) aflexible, transparent, heat-resistant, polymeric supporting base member,(b) a thermoplastic layer consisting essentially of a solid complexepoxide resin of average molecular weight between 1500 to 4000comprising the product of reaction of resorcinol and epichlorohydrin,and (c) an intermediate transparent conducting layer be tween the basemember and the thermoplastic layer.

4. An optically clear recording film consisting essentially of (l) aflexible, transparent, heat resistant polyethylene terephthalatesupporting base member, (2) an outer thermoplastic layer consistingessentially of a solid complex epoxide resin, of average molecularweight between 1500 to 4000 comprising the product of reaction ofepichlorohydrin and bis-(4-hydroxyphenyl)-2,2-propane,

i l. and (3) an intermediate transparent conducting layer between thebase member and the thermoplastic layer comprising chromium.

5. An optically clear recording film consisting essentially of (1) aflexible, transparent, heat resistant polyethylene terephthalatesupporting base member, (2) an outer thermoplastic layer consistingessentially of a solid complex epoxide resin of average molecular weightbetween 1500 to 4000 comprising the product of reaction ofepichlorohydrin and resorcinol, and (3) an intermediate transparentconducting layer between the base member and the thermoplastic layercomprising chromium.

6. An optically clear recording film consisting essentially of (1) aflexible, transparent, heat-resistant polycarbonate resin supportingbase member, (2) an outer thermoplastie layer consisting essentially ofa solid complex epoxide resin of average molecular weight between 1500to 4000 comprising the product of reaction of epichlorohydrin andbis(4-hydroxyphenyl)-2,2-propane, and (3) an intermediate transparentconducting layer between the base member and the thermoplastic layercomprising chromium.

References Cited in the file of this patent UNITED STATES PATENTS2,789,966 Dunham Apr. 23, 1957 2,985,866 Norton May 23, 1961 3,009,847Alles et al -2 Nov. 21, 1961

1. AN OPTICALLY CLEAR RECORDING FILM CONSISTING ESSENTIALLY OF (A) AFLEXIBLE, TRANSPARENT, HEAT RESISTANT, POLYMERIC BASE SUPPORTING MEMBER,(B) A THERMOPLASTIC LAYER CONSISTING ESSENTIALLY OF A SOLID COMPLEXEPOXIDE RESIN OF AVERAGE MOLECULAR WEIGHT BETWEEN 1500 TO 4000CONTAINING EPOXY GROUPS AND COMPRISING A POLYETHER DERIVATIVE OF APOLYHYDRIC AROMATIC COMPOUND CONTAINING AT LEAST